As you can see, I open a new x-windw and change resolution on the go. Sometimes, thoug, some of the games will freeze, and the x-window wont die, even if the game is closed.
Usually, I can kill x with ctr-alt-bkspace, but this will work in tt7(default) only. In tty8the command will not work.

So, I want to know, is there a way to restrat or kil the x-window process taking place in tty8

This will work most of the time, this is why I accept this answer. In this current case the app is working on its on in the new X window, so alt+f2 cannot bring command line :)
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deckoffFeb 9 '12 at 23:30

No, nothing happens, I added it, checked the file, the was correctly changed, restarted, but still this key combination will not work. I think I can write a simple bash script to find xorg process running at tty8 and kill it. kill -9 some number will kill it
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deckoffFeb 9 '12 at 16:50